Scientists have long suspected that THC somehow affects the hippocampus region of the brain, the bit responsible for controlling short-term memory, but they have never been able to prove it. Turns out that's because they were looking at the wrong grey matter.

A duo of researchers—Giovanni Marsicano of the University of Bordeaux, France, and Xia Zhang of the University of Ottawa Institute of Mental Health Research—have been credited with the discovery, published in the journal Cell. Previously, scientists believed that THC "loosened" synapses in the hippocampus, resulting in memory loss. But, contrary to convention, the effect isn't rooted in the drug's effect on the neurons alone but also on an undiscovered reaction between THC and non-neuronal cells known as astrocytes.

Astrocytes used to be thought of simply "support" cells that helped neurons function. However, the team's research showed that these cells also produce a chemical called AMPA when they interact with THC and it's the AMPA compound that can mitigate or enhance the looseness of the neuron's synapse.

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To prove the hypothesis, the team employed three types of rats with various alterations to their neurons' CB1 receptors (these receptors bind with THC and activate the cells when THC is present). The first set lacked receptors on cells that produce the neurotransmitter glutamate, the second set lacked receptors on cells that create the neurotransmitter GABA, and the third set lacked them on the AMPA-producing astrocytes. Basically, if the cells lacked this receptor, THC wouldn't affect them and they wouldn't produce the associated chemical.

The team inserted electrodes into the anesthetized rats' brains, got them blunted, and then recorded the results. The glutamate and GABA sets of rats responded in the same way that normal rats would—high as shit and terrible short-term memory. The AMPA-less rats however were unaffected.

So hey, great, they've figured out how to get rats high but not forget what they were just doing. How does that affect the average toker in the street? It's actually kind of a big deal, since science had no clue that astrocytes did much more than sit there. It opens up an entire new avenue of neuroresearch and Marsicano envisions this discovery leading to THC-derived pain-killers that don't affect working memory—think Ambien without all the pesky sleep-driving.

And for tokers looking to take advantage of this discovery—right now, before you forget—should check with their local dispensary for strains containing high concentrations of cannabidiol. A 2010 study noted that strains high in it didn't produce the impairing side effect. [Nature]